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Forte Audio 1A problems... PLEASE HELP!!
Forte Audio 1A problems... PLEASE HELP!!
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Old 14th August 2017, 07:01 PM   #21
Randy Y is offline Randy Y  United States
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Default didn't help

Sorry for the delay getting back but I hurt my back and had to stop doing everything. I put 10 times the resistance across R14 and it didn't make any changes to the bias. It is still showing no bias at all across resistors. Thanks for your help.
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Old 11th September 2017, 07:30 PM   #22
Randy Y is offline Randy Y  United States
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Default finally found problem

Old insulators on outputs were bad letting ground short out driver. Should have replaced those at first but I didn't do it.
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Old 15th November 2017, 12:13 AM   #23
scintillantorange is offline scintillantorange
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Does anyone happen to know the value of the bias resistors in the Forte 1a? Mine have gotten pretty ragged and I have to keep twisting the wiper on one of the channels to get it to bias up again. I want to get replacements, I suppose I could pull one and measure it but if anyone happens to know the value I'd appreciate it. Thanks!
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Old 15th November 2017, 01:09 AM   #24
Zen Mod is offline Zen Mod  Serbia
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Forte Audio 1A problems... PLEASE HELP!!
isn't it written in some funny way , on them?
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Old 15th November 2017, 02:50 AM   #25
Joe Berry is offline Joe Berry  United States
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Quote:
Originally Posted by scintillantorange View Post
Does anyone happen to know the value of the bias resistors in the Forte 1a?
If you mean the emitter resistors in the output stage, they are all marked 0.47 ohms. If you mean the resistors in the Vbe multiplier circuit, they are identified in the manual as R11 (1K), R12 (6.8K), R14 (1K), R15 (5K pot), and RT1 (1K thermistor). As long as you are in the mood, I would definitely replace the pot.
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Old 15th November 2017, 05:45 PM   #26
scintillantorange is offline scintillantorange
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Thanks so much for your fast responses, Zen Mod and Joe Berry! In fact, there is writing on the pots but I wasn't able to decipher it as anything to indicate value, and Google search turns up nothing that I could find helpful. I'm sure it tells the info somehow, but heck if I can figure it out.

In any case, it appears the answer is that it is a 5K pot, thank you Joe Berry! I will replace them.

I bought this amp new in the early 90's, have listened to it virtually every day since. I'm continually delighted, even near 30 years on, by the sound of music through it. How many things that you buy can you say something like that about?

Thank you again for your help!
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Old 16th November 2017, 09:12 PM   #27
Nelson Pass is offline Nelson Pass  United States
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Forte Audio 1A problems... PLEASE HELP!!
You can pretty much bet that the bias pot in any bias circuit I did is 5K.

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Old 26th December 2017, 09:05 PM   #28
Badbrad is offline Badbrad
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So, with the information I found here, I fixed my cold Model 3 problem. I checked the voltage across the resistors to start... 5 millivolts on one side, 2 on the other. I'm pretty sure these are just dirty pots that needed to be moved a touch. Adjusted them up to 25 millivolts. After 1 hour, I see about 40C on the fins. I put it back into my system and it sounds much better. The pots are super touchy. It's quite hard to get the 2 sides the same. I will try this for a bit... but I think I'm already feeling the need to try it a bit hotter. AND, what a cool thing to get a note from Mr. Pass. It adds some fun and comfort to us newbies! I'd love to buy a second model 3 if anyone has one for sale.
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Old 26th December 2017, 09:17 PM   #29
Zen Mod is offline Zen Mod  Serbia
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Forte Audio 1A problems... PLEASE HELP!!
then replace trimpots - try to preset them to same value as trimpot pulled from pcb

use appropriate multiturn pots , even if general consensus here is that multiturns are for Sissies

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